Replace SQLite with PostgreSQL for production, add Testcontainers for tests

[devin-ai-integration]

Replace SQLite with PostgreSQL for production, add Testcontainers for tests

Summary

Introduces Spring profiles to support multiple database backends:

• dev profile (default): SQLite via file-based dev.db — preserves existing local development experience
• prod profile: PostgreSQL with externalized config via environment variables
• test profile: Testcontainers spins up a disposable PostgreSQL 14 container per test run

Key changes:

• Datasource config moved from application.properties into profile-specific files (application-dev.properties, application-prod.properties, application-test.properties)
• Flyway migrations split into vendor-specific directories (db/migration/sqlite/, db/migration/postgresql/)
• MyBatis mapper SQL updated for cross-database compatibility: LIMIT x,y → LIMIT y OFFSET x, and table alias AT renamed to ATAG (reserved keyword in PostgreSQL)
• @Sql cleanup added to DbTestBase and ArticleRepositoryTransactionTest for test data isolation across shared Testcontainers instance
• docker-compose.yml added for running the app with PostgreSQL locally

Review & Testing Checklist for Human

• The original db/migration/V1__create_tables.sql was NOT deleted. If no profile is active or spring.flyway.locations is unset, Flyway could pick up both the old and new migrations. Verify whether this file should be removed or if the profile-based spring.flyway.locations always takes precedence.
• PostgreSQL migration has no foreign key constraints — this was intentional to avoid breaking tests that insert rows with fake IDs (e.g., "123", "456"). Decide if this is acceptable for production or if a follow-up V2__add_foreign_keys.sql migration is needed.
• CI requires Docker for Testcontainers. The GitHub Actions workflow (gradle.yml) was not modified. ubuntu-latest includes Docker, but confirm tests pass in CI and don't time out waiting for container startup.
• docker-compose.yml references build: . — ensure the existing Dockerfile works with the new SPRING_PROFILES_ACTIVE=prod environment variable.
• Manually test the dev profile (./gradlew bootRun) to confirm SQLite still works as expected for local development.

Notes

• Requested by: @doristian23
• Link to Devin run

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[devin-ai-integration]

Devin Review found 1 potential issue.

View 4 additional findings in Devin Review.

[devin-ai-integration]

🔴 countArticle query still uses reserved keyword AT as table alias, breaking PostgreSQL

The countArticle query in ArticleReadService.xml at lines 68-69 still uses AT as the alias for article_tags. While the PR renamed AT → ATAG in the selectArticleData and selectArticleIds SQL fragments, the countArticle query has its own inline join that was missed.

Root Cause and Impact

AT is a reserved keyword in PostgreSQL. The other queries in this file were correctly updated to use ATAG (lines 23, 24, 32, 33), but the countArticle query at lines 68-69 was overlooked:

left join article_tags AT on A.id = AT.article_id
left join tags T on T.id = AT.tag_id

This query is used to count the total number of articles matching filter criteria (by tag, author, or favorited-by). When running against PostgreSQL (both prod and test profiles), this query will fail with a syntax error because AT is a reserved keyword.

Impact: The article listing/filtering endpoints that call countArticle (to return total counts for pagination) will throw SQL exceptions on PostgreSQL, making pagination broken in production and tests.

(Refers to lines 68-69)

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